Conventionally, photolithography techniques that use i-line radiation (365 nm) use mainly positive photoresist compositions comprising an alkali-soluble resin and a quinonediazide group containing compound as a photosensitizer in the production of semiconductor elements and liquid crystal elements and the like. These positive photoresist compositions display the type of characteristics required to be equal to actual use within the fields of semiconductor element or liquid crystal element production. However, in fields that require a thick film process, for example, fields relating to magnetic heads such as giant magnetoresistive (GMR) heads or magnetoresistive (MR) heads, and particularly in the formation of the upper pole of a recording head (a magnetic head), a space pattern with a high aspect ratio must be able to be formed with good perpendicularity under thick film conditions of at least 3 μm, and formation of a resist pattern with good perpendicularity under such thick film conditions using a conventional i-line positive photoresist composition is difficult.
On the other hand, the addition of dissolution promoters (low molecular weight compounds with a phenolic hydroxyl group) to positive photoresist compositions has also been proposed. For example, the patent reference 1 discloses a positive resist composition comprising an alkali-soluble resin, a quinonediazide compound as a radiation sensitive component, and a specific compound with a phenolic hydroxyl group. Furthermore, the patent reference 2 discloses a positive photoresist composition comprising an alkali-soluble novolak resin with reduced quantities of the components with a molecular weight of less than 1000, a quinonediazide compound, and a specific compound with a phenolic hydroxyl group. However with these resist compositions, formation of a pattern with excellent resolution and good perpendicularity under thick film conditions of at least 3 μm is difficult.
Furthermore, the patent references 3 to 6 disclose positive photoresist compositions comprising an alkali-soluble novolak resin in which a portion of the hydrogen atoms of all the phenolic hydroxyl groups have been substituted with 1,2-naphthoquinonediazidesulfonyl groups as materials suitable for exposure processes under thick film conditions.
However, according to investigations conducted by the inventors of the present invention, resist compositions of this type containing an added dissolution promoter such as a typical tris-phenol based dissolution promoter suffer from a marked deterioration in heat resistance, or an inability to achieve an inadequate exposure margin, making the control of dimensions relative to the exposure dose difficult. Furthermore, these dissolution promoters do not display an entirely satisfactory dissolution promotion effect, making it impossible to achieve a satisfactory developing rate.
(Patent Reference 1)
Japanese Patent (Granted) Publication No. 2,629,990
(Patent Reference 2)
Japanese Patent (Granted) Publication No. 3,391,471
(Patent Reference 3)
Japanese Unexamined Patent Application, First Publication No. 2001-312052
(Patent Reference 4)
Japanese Unexamined Patent Application, First Publication No. 2001-312059
(Patent Reference 5)
Japanese Unexamined Patent Application, First Publication No. 2001-312060
(Patent Reference 6)
Japanese Unexamined Patent Application, First Publication No. 2001-312066